1. Field of the Invention
The present invention relates to a shock sensor for activating airbag and seatbelt systems by detecting the shock given to a car body upon, for example, automobile accidents or the like.
2. Related Art
Conventionally, shock sensors using, for example, magnetic reed switches were often used as shock sensors of this type and were structured, for example, as shown in FIG. 10.
That is, a conventional shock sensor 1 in FIG. 10, which may be installed in the body of an automobile, is constructed of a case 2, a hollow cylindrical tube 3 placed so as to extend along the direction in which the shock is to be detected (e.g. forward and backward direction ofthe automobile) within case 2, a magnetic reed switch 4 inserted into the left area within tube 3, an annular magnet 5 movably attached along the lengthwise direction of tube 3, and a spring 6 for applying force to magnet 5 in the rightward direction in FIG. 10.
The two connecting terminals of magnetic reed switch 4 are connected to an adequately structured detection circuit via lead wires not shown.
According to shock sensor 1 constructed as above, when an automobile or the like which has shock sensor 1 installed therein is still or running at an ordinary speed, magnet 5 is pressed against the right end of tube 3 by the tension of the spring. Ordinary acceleration ofthe automobile will not greatly affect shock sensor 1. Therefore, magnet 5 is separated apart from magnetic reed switch 4 inserted into the left area within tube 3. Thus, magnetic reed switch 4 is in the "off" position as it is uninfluenced by the magnetic force of magnet 5.
From this state, for example, if an automobile suddenly stops due to an accident or the like which occurred while such automobile was running and a shock is given thereby, magnet 5 is subject to a relatively large negative acceleration since shock sensor 1 is suddenly stopped from a condition wherein it was moving in the leftward direction as shown with the arrow in FIG. 10. Therefore, magnet 5 will be subject to inertial force facing relatively in the leftward direction in relation to tube 3 pursuant to the inertial mass thereof.
The inertial force moves magnet 5 leftward while resisting the tension of spring 6. When the magnetic force of magnet 5 acting on the contact of magnetic reed switch 4 becomes larger than a prescribed value, the contact of magnetic reed switch 4 is switched to the "on" position by the magnetic force of magnet 5. If the shock is large enough, magnet 5 continues moving leftward and stops when spring 6 reaches a completely compressed position. The kinetic energy accumulated on magnet 5 up to this point is temporarily converted to deformation or vibrational energy of spring 6 or case 2 and is subsequently reconverted to kinetic energy of magnet 5 when magnet 5 reverses its direction.
Thereafter, when the acceleration of magnet 5 becomes less than a prescribed value by the automobile or the like coming to a halt, magnet 5 is unable to resist the tension of spring 6 and moves rightward on tube 3 pursuant to the tension of spring 6 and is returned to its original position. When the magnetic force of magnet 5 acting on the contact of magnetic reed switch 4 becomes less than a prescribed value, the contact of magnetic reed switch 4 is switched back to the "off" position.
Thus, magnetic reed switch 4 maintains the "on" position only during the period when it is switched to the "on" position until it is switched back to the "off" position. This "on" position is detected by the connected detection circuit thereby activating the airbag and seatbelt systems. Thus, the safety of automobile passengers is secured.
However, in shock sensor 1 with this type of construction, numerous parts are necessary which lead to increased costs for shock sensor 1. Moreover, numerous steps required for assembly result in decreased productivity and increased production costs.
A further problem with conventional shock sensor 1 as depicted in FIG. 10 is that the overall size is large due to the existence of movable magnet 5.
Additional conventional shock sensors are disclosed, for example, in Japanese Patent Laid Open Publication No. Hei 8 (1996)-221665 and Japanese Patent Laid Open Publication No. Hei 9 (1997)-35598.
The shock sensor according to Japanese Patent Laid Open Publication No. Hei 8 (1996)-221665 detects vibrations generated upon glass and metals being destroyed and the shock sensor according to Japanese Patent Laid Open Publication No. Hei 9(1997)-35598 detects the tilting of objects.